The present invention relates, in general, to battery charger circuits, and more particularly to output stage circuits.
One type of battery charger is a pulsed battery charger. A pulsed battery charger provides charge to a battery on an intermittent or periodic basis. In general, this type of charger incorporates voltage sense circuitry, control circuitry, and drive circuitry. The voltage sense circuitry senses the voltage of the battery. The control circuitry determines how the battery is charged based on the sensed battery voltage. The driver circuitry provides the required current to charge the battery. Periodic or intermittent charging is achieved with a switchable current source.
An application where a pulsed battery charger is needed is in charging rechargeable alkaline batteries. Rechargeable alkaline batteries require precise charging to a predetermined voltage in order to attain maximum use between chargings. Overcharging this type of battery by more than a few millivolts may cause battery damage. The rechargeable alkaline batteries have a high series resistance that produces a voltage drop in series with the battery voltage. Sensing the battery voltage when charging is not easily accomplished. Pulse charging provides an accurate way of sensing battery voltage. The voltage is sensed between pulses when the battery is not being charged thereby providing an accurate measurement of the battery voltage. The average charging current of the battery charger can be controlled by the duty cycle of the pulse charging system.
Most battery chargers are manufactured for simplicity and to reduce costs. Standard battery chargers do not provide the precise control needed to charge a rechargeable alkaline battery without damage or shortening the number of times it can be charged. It would be of great benefit, if a battery charger output stage circuit is provided that could charge a battery to a precise voltage.